| Date | May 2011 | Marks available | 1 | Reference code | 11M.2.HL.TZ2.2 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Identify | Question number | 2 | Adapted from | N/A |
Question
The diagram below shows two nucleotides linked together to form a dinucleotide.
Identify the chemical group labelled I.
State the type of bond labelled II.
Distinguish between the sense and antisense strands of DNA during transcription.
Compare the DNA found in prokaryotic cells and eukaryotic cells.
Markscheme
phosphate
covalent / phosphodiester
only the antisense strand is transcribed / the antisense strand is transcribed to mRNA and the sense strand is not transcribed/has the same base sequence as mRNA (with uracil instead of thymine)
To award [1], reference must be made to both strands and transcription.
Award marks for paired statements only. Answers do not need to be shown in a table format.
Examiners report
In part (i), virtually all students identified the phosphate group.
Most were also able to identify the covalent or phosphodiester bond, although some stated it was an H bond.
This question was difficult for most students, although some wrote correct answers. In some scripts, students answered in terms of 3' → 5', whereas others did not refer to the two strands, nor did they relate them to transcription.
Few students got full marks as they did not compare relative characteristics. For example, it appears that many candidates interpret "naked" DNA as not being within a nuclear envelope. With this assumption, it is more difficult for them to gain mark on correct pairs of statements.
